Activated carbon technology is widely used in processes for solvent recovery and air pollution abatement. In some applications, e.g., adsorption of organic vapors from air streams, an activated carbon bed containing adsorbed organic compounds is operated in the presence of oxygen.
Incidents of runaway exothermic reactions and combustion of adsorbent beds have been reported under conditions wherein an oxidizable organic compound, e.g., a ketone, aldehyde or organic acid, is adsorbed in an activated carbon bed in the presence of oxygen, see, e.g., E. C. Akubuiro, N. J. Wagner, "Assessment of Activated Carbon Stability Toward Adsorbed Organics", Ind. Eng. Chem. Res. 31, 339-346 (1992); A. A. Naujokas, "Spontaneous Combustion of Carbon Beds", Plant/Operations Progress Vol. 4, No. 2 (April 1985); A. A. Naujokas, "Preventing Carbon Bed Combustion Problems", Loss Prev., 1978 (12), 128-135.
The combustion phenomenon presents a particularly severe problem in applications where activated carbon bed adsorption is used to recover cyclohexanone, see, e.g., M. Mizutani, M. Minemoto and M. Hirao, "Prevention of the Ignition Phenomenon of Activated Carbon Beds During Recovery of Solvent Containing Cyclohexanone", Kagaku Kogaku Ronbushu, 16 (1), 23-30 (1990); Y. Takeuchi, M. Mizutani and H. Ikeda, "Prevention of Activated Carbon Bed Ignition and Degradation During the Recovery of Cyclohexanone", Journal of Chemical Engineering of Japan Vol. 23, No. 1, 68-74 (1990).
The carbon bed combustion problem has been addressed by the addition of moisture to the gas stream, see, e.g., Takeuchi et al, above, and by purging the bed with an inert gas during shutdown, see, e.g., Mizutani et al, above. However, each of these approaches may detrimentally affect the operating efficiency of the bed, i.e., moisture in the gas stream reduces capacity of the adsorbent for adsorbing organic compounds and an inert purge gas stream effectively forces the mass transfer region of the bed toward the outlet of the bed.